Evolution of 17-β-estradiol, estrone and estrone-sulfate concentrations in late pregnancy of different breeds of mares using Liquid Chromatography and Mass Spectrometry

This study describes 17-β-estradiol (E2), estrone (E1) and estrone-sulfate (E1S) concentrations between 4 and 11 months in healthy equine pregnancies of two different breeds using Liquid Chromatography coupled to Mass-Spectrometry (LC-MS). In 2 stud-farms including 15 Spanish PureBred (SPB) and 11 Showjumping (SJ) types mares, combined thickness of the uterus and the placenta (CTUP) was measured and blood was sampled monthly between 4 and 11 months of gestation. Concentrations of E2, E1 and E1S were assayed with LC-MS in mares with normal CTUP. Effects of breed, day of pregnancy and mare's parity and age on estrogens concentrations were investigated. Peak of E2 was observed at 5 months (median: 46.4 pg/mL; maximum: 201.5 pg/mL). A strong correlation was observed between E1 and E1S (p < 0.0001, r = 0.85). Peak of E1 (median: 571.0 pg/mL; maximum: 1641.9 pg/mL) and E1S (median: 573.6 ng/mL; maximum: 997.6 ng/mL) concentrations was observed at the 5th month and then E1S decreased quicker than E1 until the end of pregnancy. Higher E2 and E1 concentrations were observed in SJ than in SPB mares between the 6th and the 8th months. No difference between breeds was observed for E1S monthly evolution. Estrogen peak values were all observed at 5 months. Unlike recent LC-MS studies, E1S values observed here were in the same range than those previously established using immuno-assays. After the 6th month, E1S decreased quicker than E1. Effect of breed only observed on non-sulfonated estrogens should be further confirmed. These findings confirm that sulfonation activity of the allantochorion may be limited after the 6th month.

Assessment of serum total 25-hydroxyvitamin D assays for Vitamin D External Quality Assessment Scheme (DEQAS) materials distributed at ambient and frozen conditions

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes human serum samples four times per year to over 1000 participants worldwide for the determination of total serum 25-hydroxyvitamin D [25(OH)D)]. These samples are stored at -40 °C prior to distribution and the participants are instructed to store the samples frozen at -20 °C or lower after receipt; however, the samples are shipped to participants at ambient conditions (i.e., no temperature control). To address the question of whether shipment at ambient conditions is sufficient for reliable performance of various 25(OH)D assays, the equivalence of DEQAS human serum samples shipped under frozen and ambient conditions was assessed. As part of a Vitamin D Standardization Program (VDSP) commutability study, two sets of the same nine DEQAS samples were shipped to participants at ambient temperature and frozen on dry ice. Twenty-eight laboratories participated in this study and provided 34 sets of results for the measurement of 25(OH)D using 20 ligand binding assays and 14 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. Equivalence of the assay response for the frozen versus ambient DEQAS samples for each assay was evaluated using multi-level modeling, paired t-tests including a false discovery rate (FDR) approach, and ordinary least squares linear regression analysis of frozen versus ambient results. Using the paired t-test and confirmed by FDR testing, differences in the results for the ambient and frozen samples were found to be statistically significant at p < 0.05 for four assays (DiaSorin, DIAsource, Siemens, and SNIBE prototype). For all 14 LC-MS/MS assays, the differences in the results for the ambient- and frozen-shipped samples were not found to be significant at p < 0.05 indicating that these analytes were stable during shipment at ambient conditions. Even though assay results have been shown to vary considerably among different 25(OH)D assays in other studies, the results of this study also indicate that sample handling/transport conditions may influence 25(OH)D assay response for several assays.

Vitamin D Standardization Program (VDSP) intralaboratory study for the assessment of 25-hydroxyvitamin D assay variability and bias

An intralaboratory study assessing assay variability and bias for determination of serum total 25-hydroxyvitamin D [25(OH)D] was conducted by the Vitamin D Standardization Program (VDSP). Thirteen assays for serum total 25(OH)D were evaluated in a single laboratory including 11 unique immunoassays and one liquid chromatography - tandem mass spectrometry (LC-MS/MS) assay. Fifty single-donor serum samples, including eight samples with high concentrations of 25(OH)D₂ (> 30 nmol/L), were assigned target values for 25(OH)D₂ and 25(OH)D₃ using reference measurement procedures (RMP). Using four replicate measurements for each sample, the mean total percent coefficient of variation (%CV) and mean % bias from the target values were determined for each assay using the 50 single-donor samples and a 42-sample subset, which excluded 8 high 25(OH)D₂ concentration samples, and compared with VDSP performance criteria of ≤ 10 % CV and ≤ ±5 % mean bias. All 12 assays achieved the performance criterion for % CV, and 9 of the 12 assays were within ≤ ±5 % mean bias. The Fujirebio Inc. assay exhibited the lowest %CV and highest percentage of individual measurements within ≤ ±5 % mean bias. Ten immunoassays exhibited changes in response due to the high 25(OH)D₂ samples with Abbott, Biomérieux, DiaSorin, DIAsource, and IDS-iSYS assays having the largest deviations. The Fujirebio Inc. and Beckman Coulter assays were only minimally affected by the presence of the high 25(OH)D₂ samples. Samples with high concentrations of 25(OH)D₂ provided a critical performance test for immunoassays indicating that some assays may not have equal response or recovery for 25(OH)D₂ and 25(OH)D₃.

Interlaboratory comparison of 25-hydroxyvitamin D assays: Vitamin D Standardization Program (VDSP) Intercomparison Study 2 - Part 1 liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays - impact of 3-epi-25-hydroxyvitamin D3 on assay performance

An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays used for the determination of serum total 25-hydroxyvitamin D (25(OH)D), which is the sum of 25-hydroxyvitamin D₂ (25(OH)D₂) and 25-hydroxyvitamin D₃ (25(OH)D₃). A set of 50 single-donor samples was assigned target values for concentrations of 25(OH)D₂, 25(OH)D₃, 3-epi-25-hydroxyvitamin D₃ (3-epi-25(OH)D₃), and 24R,25-dihydroxyvitamin D₃ (24R,25(OH)₂D₃) using isotope dilution liquid chromatography - tandem mass spectrometry (ID LC-MS/MS). VDSP Intercomparison Study 2 Part 1 includes results from 14 laboratories using 14 custom LC-MS/MS assays. Assay performance was evaluated using mean % bias compared to the assigned target values and using linear regression analysis of the test assay mean results and the target values. Only 53% of the LC-MS/MS assays met the VDSP criterion of mean % bias ≤ |±5%|. For the LC-MS/MS assays not meeting the ≤ |±5%| criterion, four assays had mean % bias of between 12 and 21%. Based on multivariable regression analysis using the concentrations of the four individual vitamin D metabolites in the 50 single-donor samples, the performance of several LC-MS/MS assays was found to be influenced by the presence of 3-epi-25(OH)D₃. The results of this interlaboratory study represent the most comprehensive comparison of LC-MS/MS assay performance for serum total 25(OH)D and document the significant impact of the lack of separation of 3-epi-25(OH)D₃ and 25(OH)D₃ on assay performance, particularly with regard to mean % bias.

Assessment of serum total 25-hydroxyvitamin D assay commutability of Standard Reference Materials and College of American Pathologists Accuracy-Based Vitamin D (ABVD) Scheme and Vitamin D External Quality Assessment Scheme (DEQAS) materials: Vitamin D Standardization Program (VDSP) Commutability Study 2

An interlaboratory study was conducted through the Vitamin D Standardization Program (VDSP) to assess commutability of Standard Reference Materials® (SRMs) and proficiency testing/external quality assessment (PT/EQA) samples for determination of serum total 25-hydroxyvitamin D [25(OH)D] using ligand binding assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A set of 50 single-donor serum samples were assigned target values for 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] using reference measurement procedures (RMPs). SRM and PT/EQA samples evaluated included SRM 972a (four levels), SRM 2973, six College of American Pathologists (CAP) Accuracy-Based Vitamin D (ABVD) samples, and nine Vitamin D External Quality Assessment Scheme (DEQAS) samples. Results were received from 28 different laboratories using 20 ligand binding assays and 14 LC-MS/MS methods. Using the test assay results for total serum 25(OH)D (i.e., the sum of 25(OH)D2 and 25(OH)D3) determined for the single-donor samples and the RMP target values, the linear regression and 95% prediction intervals (PIs) were calculated. Using a subset of 42 samples that had concentrations of 25(OH)D2 below 30 nmol/L, one or more of the SRM and PT/EQA samples with high concentrations of 25(OH)D2 were deemed non-commutable using 5 of 11 unique ligand binding assays. SRM 972a (level 4), which has high exogenous concentration of 3-epi-25(OH)D3, was deemed non-commutable for 50% of the LC-MS/MS assays.

[How to estimate glomerular filtration rate in the context of drug dosage adaptation ?]

In chronic kidney disease (CKD) patients, the dosage of many medications should be adapted according to the glomerular filtration rate (GFR). GFR estimation is obtained by using creatinine-based equations. Many different equations have been proposed in the literature, and they don't systematically lead to the same result in terms of drug dosage. There is an ongoing debate to determine which equations should be recommended, with the Cockcroft equation on one side and the MDRD (« Modified Diet in Renal Diseases ») or CKD-EPI (« Chronic Kidney Disease Epidemiology ») on the other side. The last two equations are especially used by nephrologists whereas the Cockcroft is still considered by geriatrists and pharmacologists. In the current article, we discuss the pro/cons from both sides, and propose recommendation for the clinical practice.

Establishment of reference intervals for serum concentrations of androstanediol glucuronide by a newly developed LC-MS/MS method

BACKGROUND

Androstanediol glucuronide is linked to a range of disorders of peripheral androgen formation and action, such as in hirsutism and acne. Nowadays its accurate quantification is still challenging and there are just a few LC-MS/MS methods available. Besides, their reference intervals for normal European populations by LC-MS/MS, including prepubertal and pubertal children, have not been reported yet.

METHODS

Validation of the proposed new methodology was performed at 3 levels in triplicate during 3 different days. Calibration curve concentration ranged from 0.1 to 25 µg/L. For method comparison between ELISA and the newly developed LC-MS/MS method, 43 patient samples were tested. A reference interval study was performed with 264 healthy Belgian individuals (108 male and 156 female).

RESULTS

Validation of the proposed LC-MS/MS method was satisfactorily achieved, with mean imprecision values lower than 7.4%, mean recoveries within 99-108% and a limit of quantification of 0.059 µg/L. Compared to LC-MS/MS, ELISA showed a positive bias in serum samples, providing results 43% higher for the same sample. As a consequence, new reference intervals based on age and gender have been calculated.

CONCLUSION

An easy, fast and straightforward LC-MS/MS method for the determination of androstanediol glucuronide has been developed and fully validated. Besides, reference interval for normal European populations, including prepubertal and pubertal children has been established for the first time.

[Hypercalcemia and inactive mutation of CYP24A1. Case-study and literature review]

We present the case of a family whose members have high levels of serum calcium (hypercalcaemia) by loss of function of the enzyme vitamin D 24-hydroxylase due to bi-allelic mutations in the CYP24A1 gene: c.443 T>C (p.Leu148Pro) and c.1187 G>A (p.Arg396Gln). 24-VITD hydroxylase is a key player in regulating the circulating calcitriol, its tissue concentration and its biological effects. Transmission is recessive. The estimated prevalence of stones in the affected subjects is estimated between 10 and 15%. The loss of peripheral catabolism of vitamin D metabolites in patients with an inactivating mutation of CYP24A1 is responsible for persistent high levels of 1,25-dihydroxyvitamin D especially after sun exposure and a charge of native vitamin D. Although there are currently no recommendations (French review) on this subject, this disease should be suspected in association with recurrent calcium stones with nephrocalcinosis, and a calcitriol-dependent hypercalcaemia with adapted low parathyroid hormone levels. Resistance to corticosteroid therapy distinguishes it from other calcitriol-dependent hypercalcemia. A ratio of 25-hydroxyvitamin D/24.25 hydroxyvitamin D>50, is in favor of hypercalcemia with vitamin D deficiency 24-hydroxylase. Genetic analysis of CYP24A1 should be performed at the second step. The current therapeutic management includes the restriction native vitamin D supplementation and the limitation of sun exposure. Biological monitoring will be based on serum calcium control and modulation of parathyroid hormone concentrations.

Supplementation with 80,000 IU vitamin D3/month between November and April corrects vitamin D insufficiency without overdosing: Effect on serum 25-hydroxyvitamin D serum concentrations

INTRODUCTION

Vitamin D insufficiency, defined by a 25-hydroxyvitamin D (25OHD) serum concentration<20ng/mL, is highly frequent in the French general population, especially between November and April. The aim of this study was to evaluate whether 80,000 IU vitamin D3 every month during this period of the year was able to maintain a 25OHD level between 20 and 60ng/mL in apparently healthy subjects whatever their basal vitamin D status.

METHODS

Ninety-eight subjects volunteered to receive an 80,000 IU vitamin D3 dose every month between November 2014 and April 2015. Serum 25OHD, calcemia and calciuria were measured just before the first dose (Month 0), just before the 4th dose (M4), and one month after the 6th dose (M7).

RESULTS

At M0, 25OHD was 17.5±9.5ng/mL. Sixty subjects (61.2%) had a 25OHD<20ng/mL and 25 (25.5%) had a 25OHD<10ng/mL. 25OHD increased significantly at M4 (35.3±8.0ng/mL) and M7 (40.1±8.5) without change in calcemia and calciuria. At M4, 2 subjects had a 25OHD slightly below 20ng/mL (17.6 and 19.7ng/mL), and none had a concentration>60ng/mL. At M7, all had a serum 25OHD>20ng/mL and 2 subjects had a value slightly above 60ng/mL (62.1 and 63.2ng/mL).

CONCLUSION

A monthly supplementation with 80,000 IU vitamin D3 between November and April corrected vitamin D insufficiency in subjects in whom it was initially very frequent, without overdosing. This protocol is simple, safe and costless, and can be easily implemented when physicians detect risk factors for hypovitaminosis D in patients for whom a 25OHD measurement is not indicated.

[Dosing adjustment and renal function: Which equation(s)?]

While the CKD-EPI (for Chronic Kidney Disease Epidemiology) equation is now implemented worldwide, utilization of the Cockcroft formula is still advocated by some physicians for drug dosage adjustment. Justifications for this recommendation are that the Cockcroft formula was preferentially used to determine dose adjustments according to renal function during the development of many drugs, better predicts drugs-related adverse events and decreases the risk of drug overexposure in the elderly. In this opinion paper, we discuss the weaknesses of the rationale supporting the Cockcroft formula and endorse the French HAS (Haute Autorité de santé) recommendation regarding the preferential use of the CKD-EPI equation. When glomerular filtration rate (GFR) is estimated in order to adjust drug dosage, the CKD-EPI value should be re-expressed for the individual body surface area (BSA). Given the difficulty to accurately estimate GFR in the elderly and in individuals with extra-normal BSA, we recommend to prescribe in priority monitorable drugs in those populations or to determine their "true" GFR using a direct measurement method.

[The matrix-gla protein awakening may lead to the demise of vascular calcification]

Matrix-gla-protein (MGP) is mainly secreted by chondrocytes and smooth vascular muscle cells. This potent inhibitor of vascular calcification need to undergo 2 post-transcriptional steps to be fully active: one phosphorylation of 3 serine residues (on 5) and a carboxylation of 5 glutamate residues (on 9). Like other "Gla" proteins, this carboxylation is vitamin K dependant. Several forms of MGP thus circulate in the plasma, some of them being totally inactive (the unphosphorylated and uncarboxylated MGP), some others being partially or fully active, according to the number of phosphorylated or carboxylated sites. A theoretical link exists between MGP, vitamin K, vascular calcifications and cardiovascular diseases. This link is even more evident in patients suffering from chronic kidney diseases (CKD), and notably hemodialysis patients. If this link has been demonstrated in different experimental studies, clinical studies are mainly observational and their results must be interpreted accordingly. MGP concentrations are definitely not yet a surrogate to estimate the levels of vascular calcification, but could allow the monitoring of vitamin K treatment. Modulation of MGP concentrations may reduce vascular calcification in hemodialyzed patients, if the large ongoing trials show an efficiency of this treatment. In this review, we will summarize the role of MGP in the vascular calcifications process, describe the problems linked to the analytical determination of MGP in plasma and finally describe the different clinical studies on MGP and vascular calcifications in the general population and in CKD patients.

[Cardiovascular calcification inhibitors]

Vascular calcification is a marker of cardiovascular risk increase. Age and specific disease such as diabetes or chronic kidney disease are important factors for calcification genesis. Vascular calcification process is a complex phenomenon, involving several activators and inhibitors factors. Indeed, recent works related to in vitro and in vivo experimental studies have led to a better understanding of calcification process and identification of molecules able to modulate this system. This revue will summarize some of these molecules with a particular interest of those with therapeutic relevance. We will present: i) calcium sensing receptor and its modulation by cinacalcet; ii) pyrophosphate supplementation; iii) fetuin A and overall propensity serum test for calcification and finally; iv) matrix-Gla-protein and the use of vitamin K to prevent vascular calcification progression.

[Native vitamin D in dialysis patients]

Chronic kidney disease is frequent and usually responsible of mineral and bone disorder. These abnormalities lead to increased morbidity and mortality. To become active, native vitamin D needs a first hydroxylation in the liver, and a second one in the kidney. Next to its action on bone metabolism, vitamin D also possesses pleiotropic actions on cardiovascular, immune and neurological systems as well as antineoplastic activities. End-stage renal disease (ESRD) is also associated with a decrease in vitamin D activity by mechanisms including the increase of plasma phosphate concentration, secretion of FGF-23 and decrease in 1α-hydroxylase activity. The prevalence of 25 hydroxy-vitamin D deficiency depends on the chosen cut-off value to define this lack. Currently it is well established that a patient has to be substituted when 25 hydroxy-vitamin D level is under 30 ng/mL. The use and monitoring of 1.25 hydroxy-vitamin D is still not recommended in routine practice. The goals of vitamin D treatment in case of ESRD are to substitute the deficiency and to prevent or treat hyperparathyroidism. Interest of native vitamin D in first intention is now well demonstrated. This review article describes the vitamin D metabolism and physiology and also the treatment for vitamin D deficiency in ESRD population.

[Epidemiology of urolithiasis in Belgium on the basis of a morpho-constitutional classification]

Urolithiasis is a common condition, with a prevalence of ∼10% and a male/female ratio above 1 according to large national series. Various types of urinary stones have been described upon their mineral content and/or their morphology. Hence, a combined morpho-constitutional (M-C) classification has been proposed. In order to detail the prevalence of urolithiasis in general and of each M-C type in particular upon age and gender in Belgium, we retrospectively studied the database of a reference center for urolithiasis analysis. Between 2010 and 2013, 2195 stones were characterized. We excluded 45 non-biological stones and 281 stones, which originated from outside the study zone. Among 1869 stones, 1293 (69.2%) affected men. Prevalence peak of urolithiasis was observed between 50-60 years of age in both genders. The M-C analysis was available for 1854 stones (99.2%): multiple morphological types were concomitantly identified in 49.3%. In the whole population, the main mineral constituent was whewellite (54.4%), mainly organized as type Ia (94%). Weddellite was found in 19.8%, with an equal distribution between types IIa and IIb. Uric acid was the 3rd most frequent constituent in man, with a similar distribution between IIIa and IIIb. Phosphate was uncommon in man (8.2%), but frequent in woman (26.6%) with a type IVa1 organization. Prevalence of M-C types changes with aging, i.e. decrease of weddellite and increase of whewellite and uric acid in both genders. This retrospective analysis of a single-center database of urinary stones helps characterize the M-C epidemiology of urolithiasis in Belgium.